Hydroxyl radical (OH) is a primary oxidant in the atmosphere and affects both gasphase
pollutants and particulate matter levels. Nitrous acid (HONO) acts as an important
source of OH in the urban atmosphere. Therefore it is important to account accu-
5 rately for HONO sources within air quality models in order to predict air pollution dynamics.
HONO observations in urban areas are characterized by high concentrations
at night and low concentrations around midday. Existing gas-phase chemical mechanisms
do not reproduce the observed HONO levels, suggesting a lack of sources, such
as direct emissions or heterogeneous reactions. Specific HONO emission rates, het10
erogeneous chemical mechanisms leading to its formation and related kinetics are still
unclear. Therefore, most air quality models consider exclusively gas-phase chemistry
related to HONO. This work applies the WRF-ARW/HERMES/CMAQ modeling system
to quantify the effect of the addition of HONO sources in the predictability of HONO
profiles, and its subsequent effect on secondary pollutants formation (mainly O3 and
15 PM2.5).